1. Field of the Invention
The present invention relates to a locking mechanism for an optical module used for making optical signal communications. More specifically, the present invention relates to a locking mechanism for fixing an optical module for use in any of transmission, reception and transmission/reception of optical signals to a cage for housing the optical module.
2. Description of the Related Art
Conventionally, there is known, as an optical module for use in making optical communications, an optical transceiver which comprises a light emitting element and a light receiving element for performing an photo-electric conversion in order to make communications through optical fibers.
One type of such optical transceivers has a case which contains an optical unit including a light emitting element and a light receiving element, and is designed to be removably housed in a cage mounted on a board. An electric connector connected to the board is disposed within the case, such that when the optical transceiver is housed in the case, a connection terminal of the optical transceiver is connected to the electric connector. The optical transceiver thus configured provides for the optical communication through the conversion of optical signals communicated through optical fibers to electric signals communicated between boards, and vice versa.
However, in the optical transceiver configured as mentioned above, the optical transceiver is fixed to the case with the connection terminal of the optical transceiver connected to the electric connector within the cage, but with a fixing strength not so high. Therefore, the optical transceiver is pulled out of the case when even a slight tension is applied, for example, to an optical fiber connected to the optical transceiver. If the optical transceiver is pulled out of the case during its operation, this can cause not only the interruption of a communication in the middle but also a failure of a communication device including the optical transceiver. For this reason, the optical transceiver must be firmly fixed in the cage.
For fixing the transceiver in the cage, a locking mechanism may be used for maintaining the optical transceiver fixed in the cage. Various types of such locking mechanisms have been conventionally proposed and can be used for the purpose of fixing the transceiver in the cage, and one of such locking mechanisms available for this purpose is described in Japanese patent Laid-open Publication No. 119951/94.
FIG. 1 is a perspective view illustrating a conventional connector locking mechanism described in Japanese patent Laid-open Publication No. 119951/94.
The illustrated conventional connector locking mechanism comprises male connector A made of synthetic resin; female connector B likewise made of synthetic resin; and engaging drive lever C swingably mounted on female connector B through supporting shafts 201. Engaging drive lever C is formed with cam grooves 202, and has operating part 203 which comprises lock engaging piece 204 which in turn comprises locking protrusion 204c having tapered engaging guide surface 204a and engaging surface 204b. 
When the foregoing locking mechanism is applied to an optical transceiver, male connector A corresponds to the optical transceiver (case), and female connector B corresponds to the cage. In this event, therefore, lever C is provided on the cage side.
Driven pins 205 protrude on both side walls of male connector A, and lock 207 substantially in an L-shape is disposed in recess 206 on the outer wall of connector A. In recess 206, lock 207 has flexible lock plate 207a in an upright posture which has lock releasing part 207b extending from an upper end thereof toward the rear of male connector A. Flexible lock plate 207a is formed with locking hole 207c, and excessive displacement preventing stoppers 207d are disposed behind flexible lock plate 207a. 
A front end portion of female connector B is formed into a hood for receiving male connector A, and pin guide grooves 208 are formed on both inner surfaces of the hood for receiving driven pins 205. These pin guide grooves 208 are in alignment with inlets 202a of cam grooves 202 formed in engaging drive lever C when the latter is not operated (in the upright posture).
For connecting male connector A and female connector B to each other, driven pins 205 of male connector A are first moved through pin guide grooves 208 into cam grooves 202, respectively. Under this condition, engaging drive lever C is turned by using operating part 203 to pull male connector A into the hood of female connector B through cam grooves 202 and driven pins 205. Then, as engaging drive lever C is fully turned in this state, locking protrusion 204 is brought into engagement with lock 207.
Lock engaging piece 204 is engaged with lock 207 as a result of the following sequence. Locking protrusion 204c of lock engaging piece 204 abuts against flexible lock plate 207a of lock 207 with the aid of tapered engaging guide surface 204a to displace flexible locking plate 207a backward, while introducing into locking hole 207c, and engagement surface 204b is locked to locking hole 207c of restored flexible lock plate 207a. 
The optical transceiver can be firmly fixed in the cage when the locking mechanism as described above is used in the optical transceiver.
However, when the locking mechanism described above is used in the optical transceiver, the optical transceiver must be attached to the cage through two operations which involve inserting the optical transceiver into the cage, and pulling down lever C to bring lock engaging piece 204 into engagement with lock 207. On the other hand, the optical transceiver must be removed from the cage through operations which involve pushing lock releasing part 207b to displace flexible lock plate 207a to the rear to disengage locking protrusion 204c from locking hole 207c for releasing the optical transceiver and cage from each other, and returning lever C to the original position indicated in FIG. 1.
As described above, since the foregoing locking mechanism requires a sequence of operations for removing the optical transceiver from the cage, complicated operations are involved in the removal of the optical transceiver. Particularly, when a communication device has a multiplicity of optical transceivers, the operations become more complicated.
In recent years, a reduction in size and a higher mounting density have been increasingly promoted for most of devices including communication devices. Accordingly, like reduction in size and higher mounting density have been also implemented in optical modules such as optical transceivers disposed in the communication devices.
For mounting a plurality of optical transceivers within a communication device at a high density, the plurality of optical transceivers must be arranged adjacent to each other both in the horizontal and vertical directions. However, when the optical transceiver comprises the aforementioned locking mechanism, a space must be ensured for moving operating part 203 of lever C between positions above and in front of the cage. Consequently, the plurality of cages cannot be arranged adjacent to each other in the vertical direction, thus failing to mount a plurality of optical transceivers within a communication device at a high density.